Burnout of residual carbon in coal fly ash using air cyclones

ABSTRACT

This patent application is for the novel utilization of an air cyclone combustion unit (CCU) for burnout of residual carbon from burning of fly ash resulting from coal and/or coke in electric power plants or from natural pozzolans. In some cases, residual carbon and/or moisture is too high in fly ash or pozzolans to meet market conditions for quality or ASTM C 618 Specification for Natural Pozzolans and Coal Fly Ash. Heat treating the coal fly ash or natural pozzolan to remove sufficient amounts of carbon renders the remaining pozzolan capable of meeting specifications and being sufficient in quality to perform as a cementitious material in concrete and mortars. Use of an air cyclone, with suitable mechanical adjustments and heat either from an external source or with the inherent heat value from the residual carbon will be claimed.

REFERENCES CITED FOR THE PRIOR ART: [REFERENCED BY]

-   1. United States Patent Application 20090200156, Whellock; John G.,    Aug. 13, 2009, Treatment of fly ash from coal combustion to improve    its marketability.-   2. U.S. Pat. No. 4,527,973, Jul. 9, 1985, Precalciner for Cement Raw    Meal, Takahiko Kando, Masahiko Kitajima, Yamaguchi, Japan, assigned    to UBE Industries, Yamaguchi, Japan.-   3. U.S. Pat. No. 7,261,047 Ljungdahl, Boo, Aug. 28, 2007, Control of    cyclone burner, Assignee: TPS Termiska Processer AB (Nykoping, SE)-   4. U.S. Pat. No. 5,462,430 Khinkis Oct. 31, 1995, Process and    apparatus for cyclonic combustion, Assignee: Institute of Gas    Technology (Des Plaines, Ill.).-   5. U.S. Pat. No. 6,036,475 Matsui, Koichi (Kyoto, JP), Kuwagaki;    Isao (Kyoto, JP), Mar. 14, 2000, Cyclonic type combustion apparatus,    Assignee: Takuma Co. Ld. (Osaka, JP)-   6. U.S. Pat. No. 4,934,931, Angelo, II James Jun. 19, 1990, Cyclonic    combustion device with sorbent injection Angelo, II; F. (Little    Rock, Ark.).-   7. U.S. Pat. No. 5,220,888, Khinkis; Mark J. (Morton Grove, Ill.),    Abbasi; Hamid A. (Darien, Ill.), Jun. 22, 1993, Assignee: Institute    of Gas Technology (Chicago, Ill.).-   8. U.S. Pat. No. 4,920,925, Korenberg; Jacob (York, Pa.), Khinkis;    Mark (Morton Grove, Ill.), May 1, 1990, Assignee: Donlee    Technologies Inc., (York, Pa.).

OTHER REFERENCES

-   1. A semi-mobile flash dryer/calciner unit to manufacture pozzolana    from raw clay soils—application to soil stabilization, S. Salvador,    A and O. Ponsb, Ecole des Mines d'Albi Carmaux, Campus Jarlard, 81    013 Albi CT Cedex 09, France Entreprise MALET, 30 Avenue de Larrieu,    31 081 Toulouse Cedex France.-   2. Fluid Dynamics Applied to a Cement Precalciner, Giddings D.    Eastwick C. N; Pickering S. J; Simmons K.1, Proceedings of the I    MECH E Part A Journal of Power and Energy, Professional Engineering    Publishing, Volume 214, Number 3, 5 Jun. 2000, pp. 269-280.-   3. Flyash Beneficiation By Air Classification, J. G. Groppo    and S. M. Brooks Center For Applied Energy Research University of    Kentucky And Clarence Kreiser Buell Division of Fisher-Klosterman,    Inc.-   4. Investigation into the operation of a cement works precalciner    vessel, Donald Giddings, Thesis submitted to The University of    Nottingham for the Degree of Doctor of Philosophy, Investigation    into the operation of a cement works precalciner vessel by Donald    Giddings, Thesis submitted to The University of Nottingham for the    Degree of Doctor of Philosophy The University of Nottingham School    of Mechanical, Materials, Manufacturing Engineering and Management

FEDERALLY SPONSORED RESEARCH/DEVELOPMENT

None at this time.

BACKGROUND OF THE INVENTION

Of the 72 million tons of Coal Combustion Products (CCPs) generated bythe coal-fueled electric power industry, only about 32 million (44%) ofCCP production is beneficially used in concrete and cement products,wallboard, highway construction, and other applications. Much fly ash isunusable in concrete as it does not pass the required ASTM C 618Standard Specification for Coal Fly Ash and Raw or Calcined NaturalPozzolan for Use in Concrete. The unused proportion is increasing asmercury capture and other environmental regulations cause electric powerplant boiler techniques that render more fly ash unusable for pozzolansin concrete.

Coal-burning utilities have increasingly turned to low NOx burners toreduce nitrous oxide emissions. It is well documented that changes inthe form and quantity of unburned carbon in low NOx fly ash. Smallamounts of low-NOx carbon can lead to relatively large and variableincreases in air entraining agent (AEA) required for concrete.

Concrete is the most widely used man-made material in the world. In 2007nearly 3.05 billion tons of portland and hydraulic cement was producedworldwide. The production of cement—the main active ingredient ofconcrete—accounts for 5 to 10 percent of all anthropogenic carbondioxide emissions; a leading greenhouse gas involved in global warming.During the portland cement clinker calcining process, CaCO₃ is changedto CaO. Approximately one ton of CO₂ is released in the production ofone ton of portland cement. In the United States, portland cementproduction alone constitutes about 2-3 percent of CO₂ gasses generatedannually. Cement production generates carbon-dioxide emissions becauseit requires fossil fuels to heat the powdered mixture of limestone,clay, ferrous and siliceous materials to temperatures of 2700° F.(1,500° C.). Limestone—Calcium Carbonate (CaCO₃)—is the principleingredient of cement. During the portland cement clinker calciningprocess, CaCO₃ is changed to CaO. This conversion releases one mole ofCO₂ (carbon dioxide) for every mole of CaCO₃ consumed in the productionprocess. Approximately one ton of CO₂ is released in the production ofone ton of portland cement. In the United States, Portland cementproduction alone constitutes about 2-3 percent of CO₂ gasses generatedannually. Chemical reactions with sulfates and other mineral formationsoccur within the temperature ranges of the unit. Anhydrous calciumsulfate formed from synthetic gypsum is made by heating to a temperatureof 325°-450° C. Coal fired electric power plants have already beguncapturing mercury to comply with regulations. The Cyclonic CombustionUnit can alleviate the conditions caused by low temperature burning,additions of mercury sequestrants, elevated SOx and Ammonia. It isintended to treat fly ash or pozzolans, no matter how high theirmoisture or carbon content and reduce the organic content to a targetlevel of Loss On Ignition (LOI) in the product. Capture of mercurymetal, in it's gaseous state can be accomplished by extracting themercury from the gasses in the exhaust duct carrying gasses from thecyclone to the water spray. The mercury vapor can then cooled within aMercury Capture Unit for recovery of the mercury metal. Activated carbonto sequester Mercury is well known to cause extreme variations inconcrete quality. Variations in concrete from using such fly ash can beextreme. Much of this fly ash, now discarded, could be utilized if thequality could be improved.

Sulfates and sulfites in the CCP could be reacted with lime or othermaterials during the combustion process to render them harmless andbecome part of the mineralogy of the CCP. Likewise Ammonia (NH₄) couldbe reacted during combustion to render it harmless.

Finally, it is proposed that combustion fuel for the CCU would be wasteoil, predominantly waste engine oil further utilizing recoveredmaterials for improving the environment.

In some cases, residual carbon and/or moisture is too high in fly ash orpozzolans to meet market conditions for quality or ASTM C 618Specification for Natural Pozzolans and Coal Fly Ash. Heat treating thecoal flyash or natural pozzolan to remove sufficient amounts of carbonand/or moisture renders the remaining fly ash or pozzolan capable ofmeeting specifications and being sufficient in quality to perform as acementitious material in concrete, mortars or cementitious products.This also reduces the need for utilization of coal in portland cementproducts and inherent emission of greenhouse gasses. Coal-burningutilities have increasingly turned to low NOx burners to reduce nitrousoxide emissions. It is well documented that changes in the form andquantity of unburned carbon in low Nitrous Oxide (NOx) fly ash, as wellas the possible presence of ammonia compounds, have negatively impactedthe use of fly ash in concrete. Less well documented are possiblechanges in Low NOx fly ash that may impact strength activity indexvalues, including particle shape, size and glass content.

The carbon produced by burning coal in a plant equipped with a low-NOxburner is produced at somewhat cooler and much more reduced conditions,compared with traditional burners. The carbon associated with a low-NOxfly ash is a much more active form than that produced using traditionalburners. This highly active low-NOx carbon can adsorb liquid chemicaladmixtures used in concrete, especially the air-entraining admixtures.This can result in higher and more variable concrete air entrainingagent (AEA) dose requirements. Small amounts of low-NOx carbon can leadto relatively large increases in AEA in concrete. Variations in concretefrom using such fly ash can be extreme.

SUMMARY OF THE INVENTION

The Cyclonic Combustion Unit (CCU) invention alleviates the coal firedelectric power plant conditions caused by low temperature burning,additions of mercury sequestrants, elevated SOx and Ammonia. It isintended to treat resulting non specification or marginal quality flyash or pozzolans, no matter how high their moisture or carbon contentand reduce the organic content to a target level of Loss On Ignition(LOI) in the product. Earlier versions of this technology have been usedsince the 1970's to flash calcine kiln feed in portland cement kilns.This CCU is novel for numerous reasons including the use of plural heatsources. The CCU will reduce residual carbon and/or moisture is that toohigh in fly ash to meet market conditions for quality or ASTM C 618Specification for Natural Pozzolans and Coal Fly Ash. CCU heat treatingthe coal flyash to remove sufficient amounts of carbon renders theremaining fly ash capable of meeting specifications as a cementitiousmaterial in concrete, mortars or cementitious products. This alsoreduces the need for utilization of coal to produce portland cementproducts and inherent emission of greenhouse gasses.

Further, capture of Mercury metal, in its gaseous state is accomplished(optional) by extracting the Mercury from the exhaust duct carryinggasses from the cyclone to the water spray. The Mercury vapor can thencooled within the Mercury Capture Unit for recovery of the Mercurymetal.

Importantly, utilization of the fly ash, now discarded, will relieve theneed for extensive storage of off specification and non-useable fly ash.It would preferentially be used as a supplementary cementitiousmaterial, with it's improved quality.

As well, the use of the now discarded fly ash will reduce the amount ofcarbon dioxide emitted from production of portland cement.

Higher temperatures may be employed to further improve mineralogy of thesubject fly ash or materials fed into the unit and heat treated. Aswell, chemical reactions with sulfates and other mineral formationsoccur within the temperature ranges under consideration. For instance,anhydrous calcium sulfate form synthetic gypsum by heating to atemperature of 325°-450° C. Illite, anhydrite, quartz, anorthite,microcline, sillimanite and hematite are dominantly influenced up to700° C., and hercynite, anorthite, albite, pseudobrookite and otheriron-titanium oxides were dominant up to 1200° C. in mineralogicalformation testing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention is a duel fired counter flow air cyclone utilization for:

-   1. Burnout of residual carbon in fly ash from burning of coal in    electric power plants.-   2. Enhance fly ash and other minerals by enabling control of fly ash    residual carbon and/or moisture that is too high to meet market    conditions for quality or ASTM C 618 Specification for Natural    Pozzolans and Coal Fly Ash.-   3. CCU heat treating the coal fly ash or natural pozzolan is to    remove sufficient amounts of carbon and/or moisture and render the    resultant fly ash capable of meeting specifications. It will also be    sufficient in quality to competitively perform as a cementitious    material in concrete, mortars or cementitious products.-   4. Reduces the need for utilization of coal in portland cement    products and reduction of inherent emission of greenhouse gasses.-   5. Storage for discarded fly ash from power plants can be reduced by    the amount of fly ash treated in the proposed Coal Combustion Unit.

Conceptual Drawing (Attached in PDF) BRIEF DESCRIPTION OF THE DRAWING

Burnout of carbon in fly ash uses fuel at two locations in the cyclonesystem to reduce carbon to acceptable levels:

The unit is fed with materials metered through a feed inlet (1). Somecombustion air is also allowed to enter with the incoming feed. The unituses ignition of carbon provided by a fuel at the primary combustionzone/controllable high carbon fly ash feed inlet to the primarycombustion zone at the lower portion of the riser duct to the cyclonemain body (2). The primary combustion zone is preferentially lined withrefractory materials. A larger portion of combustion air is inlet andlarger agglomerations of feed are dropped from the inlet pipe (3).Materials dropped from the inlet pipe are removed (4) for alternate useby external equipment (5).

A fuel supplied flame (6) that may be fitted with a cone shaped nozzleto better enable oxygen for combustion to the inlet gases is installedin the inlet duct of the cyclone. Heated gases and partiallydecarbonized material are transported from the primary combustion zonethrough the cyclone inlet duct. The pipe and flame may be oriented inany fashion desirable, tangential orientation is not necessary orpreferred in order to keep heat away from any particular section of theinlet duct.

Gases move through the combustion chamber (7) and with continuingpartial and incomplete decarbonation.

Gases and materials swirl inside the cyclone (8). Cooling of thiscombustion chamber is not desired. It is preferentially lined withrefractory materials. Heat from secondary fueled flame(s) (9) consistingof one or more fuel lines and accompanying nozzles that may be outfittedwith cone shaped or atomization nozzles below the lower end of thethimble inside the cyclone completes combustion of residual carbon thatremained to the level necessary to meet customer requirements.

Material that has become agglomerated in the primary or secondaryignition zones is dropped out through an air lock system for collection(10).

Agglomerated materials and heavier particles of ash dropped from thecyclone are removed (11) for alternate use by external equipment.

A plurality of fuel lances may be employed (12).

Fly ash and remaining carbon and gasses are drawn from the cyclonethrough thimble into the cyclone outlet (13). The thimble may beadjusted in diameter or length to control the amount of heavierparticles rejected through the airlock. Oxygen can be measured to assuresafe amounts of exit oxygen (14). A mercury capture unit can be utilizedin the general location of (15).

Gases then are cooled with water spray (16) supplied by a water pipe(17). A water outlet (18) fitted to water jacket cooling unit (19)providing a cooling tunnel outfitted with a water inlet valve (20) toreduce gas exit temperature to about 115 degrees C. This same activityalso reduces the temperature of the mineral product.

The cooled and reduced carbon fly ash is then delivered to the dustcollector inlet (21). Product is collected with a dust collector (22).The dust collector is fitted with electrical or filter media to catchthe decarbonated and treated product. A discharge valve (23) is fittedto the duct collector hopper (24) to control storage and outflow of theproduct.

Product from the dust collector is delivered through a valve or feeder(25) then stored for use as a cementitious material in separate storage.Cleaned air exits the dust collector (26)

An induced draft fan (27) is used to draw ambient air through thecyclone and carry the fly ash from the cyclone in the air stream to thedust collector. Control of airflow through the cyclone allows sufficientresidence time to provide oxygen for sufficient combustion of thecarbon.

An exhaust stack (28) carries cleaned air from the unit.

DETAILED DESCRIPTION OF THE INVENTION

The proposed Cyclonic Combustion Unit (CCU) unit is a dual fired,temperature controlled, cyclonic, flow adjustable, water spray cooledexhaust gas, dust collected system for reducing carbon or improvingmineralogy in fly ash to acceptable levels. Thusly, the need forutilization of coal in portland cement products and inherent emission ofgreenhouse gasses is reduced. The cyclonic combustion unit utilizes heatfrom fuel sources employed within the primary feed section of the CCUand within the cyclone for process control of maintaining target amountsof residual carbon or complete combustion of carbon as desired. Thecarbon-laden pozzolan is fed into an air duct that is fired with fuel toacceptable temperatures. Temperatures will generally need to be in therange of 400 to 1200 degrees centigrade. The cyclone employed will allowcirculation of the fly ash and sufficient residence time to ignite andburn the carbon in the feedstock. A secondary flame inside the cyclonewill be adjusted as necessary to provide suitable reduction in carboncontent or mineralogical improvements to the feedstock fly ash resultingin controlled carbon content and mineralogy in the product. A waterspray in the exhaust duct will quench the temperature of the productfrom the cyclone. The water spray will also cool exhaust gasses tosuitable low temperatures to allow safe temperatures for the dustcollector and product handling system. A fan for the system will movethe gasses and feedstock through the CCU and draw air through the systemsupplying oxygen for fuel and carbon combustion.

Further the CCU can be operated at higher temperatures as needed and/oradditional minerals included to form mineralogical changes in thematerials fed enhancing the cementing properties of the materials fedinto the system. A stoichiometric ratio of combustion oxygen to carbonis not required or suggested.

Since the 1990s and 2000s, power plants have been equipped withadditional processes to improve air quality such as scrubbers to reduceSOx emissions, catalytic reduction equipment to reduce NOx emissions,and various systems to reduce mercury emissions. These additionalsystems have the potential to alter the fly ash with ammonia, sulfite,alkalis, and carbon residues that must be considered in selecting flyash sources, and specifying additional quality control parameters foracceptance.

Use of a counter flow air cyclone, with suitable mechanical adjustmentsand heat either from reclaimed oil source incorporated with the inherentheat value from the residual carbon will be used.

Importantly, utilization of the fly ash, now discarded, will relieve theneed for extensive storage of off specification and non-useable fly ash.It would preferentially be used as a supplementary cementitiousmaterial, with it's improved quality.

As well, the use of the now discarded fly ash will reduce the amount ofcarbon dioxide emitted from production of portland cement. Much of thisfly ash, now discarded, could be utilized if the quality could beimproved.

Utilization of every ton of fly ash improved rather than portland cementwill reduce approximately one ton of CO2 emitted

If any fraction of the approximately 40 million tons per year of fly ashnot being used can be beneficially used instead, there will be severaladvantages:

-   1. Overall carbon dioxide can be reduced. The amount of reduction is    about 1 ton net of CO2 reduced for every additional ton of fly ash    processed by a CCU.-   2. Every amount of fly ash processed by CCU does not have to be    impounded or discarded.-   3. Fly ash previously discarded or ponded could be processed and    reused as pozzolan. The amount of fly ash used from this single    activity is immense.-   4. Fly ash from the above activities can be utilized in production    of chemically activated hydraulic cements.

These chemically activated cements meet ASTM C 1600, Specification forRapid Hardening Hydraulic Cements and ASTM C 1157 Specification forStandard Performance Specification for Hydraulic Cements

The utilization of chemically activated fly ash based cements willsubstitute ton for ton with portland cement. No portland cement isneeded in concretes utilizing these cements. As well they are a provenentity.

Fly ash prepared by the CCU will have the following improvements:

-   1. Loss on Ignition (LOI) controlled to predictable and product    competitive targets.-   2. LOI control accomplished by controlling the combustion    temperature within the cyclone.-   3. Temperatures from sensors located in the feed and cyclone    combustion areas and the exit duct.-   4. Fuel is adjusted in the primary and secondary burner in the    cyclone to burn out carbon from the fly ash.-   5. Temperatures can be operated at higher temperatures to affect the    mineralogy of the fly ash.-   6. Fly ash presently failing to meet specifications or competitive    requirements of LOI can be controlled to target levels.-   7. The fly ash so treated in the CCU will not have to be placed in    landfill storage or discarded and used instead for beneficial    purposes such as replacement of portland cement in concrete. That    act further reduces the amount of CO2 produced in the substituted    cement.-   8. Fly ash presently discarded can be used instead to create    roadways, structures and other works.

1. A cyclonic combustion unit consisting of one or more cyclones orcombustion chambers outfitted with a feed mechanism to feed one or morematerials, two or more sources of fuel combustion utilizing added fuelsources, a means of cooling the resulting exit gasses and materials, adust collecting system for collecting the product of the unit and a fanfor moving gasses through the system.
 2. The combustion unit describedin claim 1 wherein said material fed into the system consists of coalfly ash, natural pozzolan, cement, cement kiln dust, slag, kaolin,bentonite, salts of metallic carbonates such as calcium, potassium,sodium, etc, hydrated lime, quicklime, clay burned lime, dirt, compostand mineral or feed stocks with compositions to modify the compositionof the fed materials either chemically or mineralogically.
 3. Thecombustion unit according to claim 1 which further comprises a chamberconnected to a feed system that has been heated with externally suppliedfuel.
 4. The combustion unit according to claim 1 that is outfitted witha system that conveys the feed from the feed and initial fueled heatsystem by air into the main body of the cyclone. The configuration ofthe combustion can be cylindrical, square or other geometricconfiguration.
 5. The combustion unit according to claim 1 that isoutfitted with an internal pipe or “thimble” reaching down into thecyclone and attached to the exhaust section of the cyclone.
 6. Thecombustion unit according to claim 5 in which the internal thimbleconnected to the exhaust section of the cyclone is adjustable in length.7. The cyclonic combustion unit in claim 3 in which is outfitted with asource of external fueled heat.
 8. The combustion unit described inclaim 1 in which the fuel may be feed into the cyclone at its peripheryor near the adjustable internal pipe.
 9. An embodiment of the cycloniccombustion system described in claim 1 in which the primary initialcombustion zone fuel is from different points of ignition and/or made upof different fuels, including natural gas, liquefied petroleum gassessuch as propane or butane, coal, coke, fuel oil, waste automotive oil orwaste cooking grease or oil.
 10. An embodiment of the cycloniccombustion system described in claim 1 in which the primary flame(s) atthe secondary combustion zone fuel in the cyclone is from differentpoints of ignition and/or made up of different fuels, including naturalgas, liquefied petroleum gasses such as propane or butane, coal, coke,fuel oil, waste automotive oil or waste cooking grease or oil.
 11. Anembodiment of the cyclonic combustion system described in claim 1 inwhich heat may be from a tertiary source such as waste heat from anothersystem.
 12. The cyclonic combustion system described in claim 1 in whichthe exhaust from the cyclone is outfitted with a duct in which there isa water spray, air, water jacket or product cooling system.
 13. Anembodiment of the cyclonic combustion system described in claim 1 inwhich there is a dust collection system consisting of a second cyclone,set of cyclones, baghouse or electrostatic precipitator to collect theproduct from the cyclone and heat treatment therein.
 14. An embodimentof the cyclonic combustion system described in claim 1 in which there isa fan to induce either heated or ambient air, oxygen in part or in totalto support combustion of the fuels used for heating the materials. 15.An embodiment of a Cyclonic Combustion Unit capable of heat treatingcoal fly ash or natural pozzolan to remove sufficient amounts of carbonand/or moisture and render the resultant fly ash capable of exhibitingpozzolanic or cementitious properties. The resulting minerals will besufficient in quality to competitively perform as a cementitiousmaterial in concrete, mortars or cementitious products.
 16. A cycloniccombustion unit according to claim 15 in which valves are inserted inthe areas at the lower end of the cyclone(s) and primary feed section toremove coarse fractions of minerals that form during combustion andhandling.
 17. An embodiment of the cyclonic combustion system describedin claim 15 in which a device is inserted into the exhaust portion ofthe cyclone to capture mercury vapors.
 18. An embodiment of the cycloniccombustion system described in claim 15 in which the fuel is provided tothe heating zones of the CCU are outfitted with pipes to which isattached a means of increasing turbulence within the flame, enablingincreased oxygen in contact with heated air for improved combustion ofcarbon or other organic materials in the feed material.
 19. Anembodiment of the cyclonic combustion system of the invention in whichsulfates and sulfites in the CCP could be reacted with lime containingmaterial added other materials at the feed inlet and minerologicallyconverted during the combustion process to render them harmless andbecome part of the mineralogy of the CCP materials product.
 20. Anembodiment of the cyclonic combustion system described in claim 19 inwhich the heated air in the stream (downstream) coming from the cycloneexhaust duct is fitted with an outer shell in which water inlet andoutlet ducts are fitted. The purpose of the outer shell is to provide awater-cooling jacket to cool the exhaust air and to some degree theheated product carried by the exhaust air.